A cathode-ray tube (CRT) has typically been used in projection technology in the past. However, CRT projectors generally have dimensions of large size and have relative low resolution, and therefore have been gradually replaced by liquid crystal display (LCD) projectors in recent years.
The liquid crystal display technology involves transmitting incident light from a light source through a trichromatic filter, then projecting three primary colors (Red, Green, Blue) to three liquid crystal display panels (LCD panels), and integrating these three primary colors to form an image. Generally speaking, the color saturation and the color temperature of the liquid crystal display projector are better. However, a transmission-type liquid crystal display panel is restricted by the light transmission ratio, which lowers the luminous efficiency compared with a reflective-type liquid crystal display panel. Besides, the size and the weight of the transmission-type liquid crystal display panel cannot be reduced due to the structure limitation of the optical engine.
Recently, another type of projection technology, i.e., a digital light processing (DLP) technology, has been developed. Detail background information of the DLP technology can be found in U.S. Pat. No. 5,658,063. The digital light processing technology was invented by Texas Instruments Incorporated located in Dallas, Tex., the United States. Different from the liquid crystal display technology, in the digital light processing technology, the light is reflected by the digital light processing chip to form an image on a surface. The key element of this technology is a semiconductor device controlled by a binary impulse adjustment, and this device is called Digital Micromirror Device (DMD).
The Digital Micromirror Device chip functions as a reflective digital optical switch, which can precisely control the light. The micromirrors of the Digital Micromirror Device in the digital light processing projector reflect the light to form an image on a surface. This technology has benefits of size and weight reductions of the projector and also provides higher luminous efficiency and higher resolution. The Digital Micromirror Device is a reflective-type optical device with high filling ratio. This property provides a higher luminous efficiency, so that the digital light processing projector can be used in areas which require high brightness and high resolution. Furthermore, the digital light processing technology has improved heat dissipation ability. This property allows the use of a light source with high watts while not decreasing the lifetime of the Digital Micromirror Device. Moreover, because the digital light processing technology is completely a digital design, the regeneration images are more stable and accurate.
In a digital light processing projector, a light pipe is an important refractive optical element. The light pipe is usually disposed between the light source and the optical engine. Generally, the light pipe is constructed by four pieces of glass. A holding device and a bracket are used to position the light pipe in the DLP projector, and screws are used to adjust the horizontal and vertical positions of the light pipe.
Refer to FIG. 1a and FIG. 1b, which are schematic diagrams of a prior art light pipe 13 disposed on an optical engine 12. As shown in FIG. 1a, the rigid holding device 11 maintains the light pipe 13 on the surface 121 of the optical engine 12 which is made of aluminum and magnesium alloy. Therefore, the light pipe 13 optically couples with the light source (not shown) in order to transmit the refracted light. Screws 14 and 15 are used to adjust the horizontal and vertical positions of the light pipe 13, respectively. As shown in FIG. 1b, the light pipe 13 is constructed of four pieces of glass held together by adhesive. The temperature at portions of the light pipe 13 close to the light source is commonly higher than those at other portions. When the temperature is over the heat resistance of the adhesive, side glass 131 and 133 of the light pipe 13 might be broken down because of side stresses.
Therefore, a heat-sinking apparatus is desired for the light pipe 13 to uniformly distribute the thermal energy generated by the light source over the light pipe 13. Moreover, a heat-sinking apparatus is desired to dissipate the thermal energy distributed over the light pipe 13, and to reduce the thermal effect on the adhesive for preventing the breakdown of the light pipe 13.